As much importance has been attached to saving in resources and countermeasures to environment in recent years, requirements to reduce fuel consumption of automobiles have been increasingly severe. Automobile tires have also been required to low their rolling resistance so as to contribute to reduction in the fuel consumption. In order to low the rolling resistance of tires, a rubber material capable of providing vulcanized rubber having high rebound resilience is used as a rubber material for the tires.
It has heretofore been proposed to use a rubber composition obtained by compounding silica as a reinforcing agent into a diene rubber in place of carbon black so as to enhance rebound resilience. However, the silica-compounded rubber composition has involved a problem that it cannot bring about sufficient abrasion resistance and tensile strength compared with the carbon black-compounded rubber composition. A cause for this problem is considered to be attributed to the fact that the affinity of the silica for the diene rubber is lower than that of the carbon black, so that a reinforcing effect cannot be sufficiently developed.
In order to enhance the affinity of the silica for the diene rubber, it has heretofore been proposed to use a silane coupling agent (Japanese Patent Application Laid-Open Nos. 252431/1991 and 252433/1991, etc.). However, this method requires to use an expensive silane coupling agent in a large amount for bringing about a sufficient effect.
It has recently been proposed to use silica surface-treated with a silicone oil having a repeating unit of --Si(CH.sub.3).sub.2 --O-- and/or --SiHCH.sub.3 --O-- (Japanese Patent Application Laid-Open No. 248116/1994). However, this method requires to conduct a heat treatment at 250.degree. C. for about 1 hour for the surface treatment of the silica, so that a sufficient effect cannot be achieved by simply kneading a diene rubber, silica and such a silicone oil in a lot in a common roll or Banbury.